Stress urinary incontinence (SUI), pelvic floor prolapse, and hernias are serious health concerns worldwide. Millions of people suffer from these problems, and surgical procedures involving the placement of implants to stabilize or support the affected tissue are required.
Devices for treating tissue defects can be constructed from synthetic materials such as polypropylene, polytetrafluoroethylene, polyester, and silicone. Devices constructed from non-synthetic materials can include allografts, homografts, heterografts, xenografts, autologous tissues, cadaveric fascia, and fascia lata. The supply of non-synthetic devices can vary greatly and certain sizes of non-synthetic materials can be difficult to obtain. For example, autologous material may be difficult or impossible to harvest from some patients due to the health of the patient or the size of the tissue needed for a repair.
Biomaterials, which work either by mechanical closure or by inducing strong scar tissue, can also be used. However, the synthetic material can increase the rate of local wound complications such as seromas (by about 30-50%), paraesthesia (by about 10-20%), and restriction of mobility (by about 25%) (see Klinge et al., Eur. J. Surg. 164:951-960, 1998). More specifically, biomaterial implants are used to support the abdominal wall, which has an average displacement elasticity of 25% at a maximum tensile strength of 16 N/cm (see Junge et al., Hernia 5:113-118, 2001). Biomaterials with initially low bending stiffness may turn into hard sheets in the post implant period and fail to exhibit 25% strain under forces of 16 N/cm. With excessive scar tissue formation, there is a decrease in abdominal wall mobility. Histological analysis of explanted biomaterials has revealed persistent inflammation at the interface, even after several years of implantation, which is influenced by the weight of the biomaterial and the surface area in contact with the recipient tissue. The persistent foreign body reaction is independent of the inflammation time, but considerably affected by the type of biomaterial (see Welty et al., Hernia 5:142-147, 2001; and Klinge et al., Eur. J Surg. 165:665-673, 1999). Consequently, the persistence of a foreign body reaction at the biomaterial-tissue interface might cause severe problems, particularly in young patients, in whom the biomaterial is expected to hold for prolonged periods of time.
Bard Mesh™ is a non-absorbable implant that is made from monofilament polypropylene fibres using a knitting process (C.R. Bard, Inc., Cranston, R.I.; see also U.S. Pat. No. 3,054,406; U.S. Pat. No. 3,124,136; and Chu et al., J. Bio. Mat. Res. 19:903-916, 1985). The thickness for Bard Mesh™ and other commercially available implants is provided in the table below. As indicated, the thinnest of these materials has a thickness of 0.016 inches.
ThicknessMaterialCompanyCode No.(inches)Bard MeshC. R. Bard/Davol1126600.026Prolene MeshJ&J/EthiconPML0.020Prolene Soft MeshJ&J/EthiconSPMXXL0.016Gore-Tex SoftW. L. Gore13150200200.079Tissue PatchProLiteAtrium Medical1001212-000.019ProLite UltraAtrium Medical307210.016
Additional non-absorbable meshes are known (see U.S. Pat. Nos. 2,671,444; 4,347,847; 4,452,245; 5,292,328; 5,569,273; 6,042,593; 6,090,116; 6,287,316 (this patent describes the mesh marketed as Prolene™; and U.S. Pat. No. 6,408,656). These products are all made using synthetic fibre technology. Different knit patterns impart unique mechanical properties to each configuration.
A variety of absorbable or partially absorbable materials have been described (see U.S. Pat. Nos. 4,633,873; 4,693,720; 4,838,884; and 6,319,264). There are also a variety of implants used to treat urinary incontinence in women (see U.S. Pat. Nos. 4,857,041; 5,840,011; 6,042,534; 6,110,101; 6,306,079; and 6,355,065; see also U.S. Pat. Nos. 5,112,344; 5,611,515; 5,637,074; 5,842,478; 5,860,425; 5,899,909; 6,039,686; 6,273,852; 6,406,423; 6,478,727; 6,702,827; WO 2004/017862; WO 02/39890; and WO 02/26108).
At present, monofilament polypropylene surgical meshes are the most widely used soft tissue implants. Although serious complications associated with implants are infrequent, they are well documented. Moreover, each of the implants presently in use are believed to have one or more deficiencies. For example, their construction can result in characteristics (e.g., wall thickness and surface area) that increase the risk of an inflammatory response or of infection; seromas can form postoperatively within the space between the prosthesis and the host tissues; due to material content, width, and wall thickness, surgeons must make large incisions for implantation (the present implants can be difficult to deploy in less invasive surgical methods); rough and irregular implant surfaces can irritate tissues and lead to the erosion of adjacent tissue structures; adhesions to the bowel can form when the implant comes in direct contact with the intestinal tract; where pore size is reduced, there can be inadequate tissue ingrowth and incorporation; and the pore size and configuration of the implants does not permit adequate visualization through the implant during laparoscopic procedures. Additional complications include pain, discomfort, obstruction, and organ perforations.